1. Field of the Invention
This invention relates to a method and an apparatus for inspecting various objects such as solder portions on a circuit board.
2. Description of the Prior Art
U.S. Pat. No. 5,103,105 discloses an apparatus for inspecting solder portions of a circuit board. In the apparatus of U.S. Pat. No. 5,103,105, a beam of light is applied to a surface of a circuit board provided with at least one solder portion. The light beam scans the surface of the circuit board. Height data are derived from a portion of the light beam which is scattered at the surface of the circuit board. The height data represents a height of a currently-scanned point of the surface of the circuit board. The height data are accumulatively added for the solder portion. A variation in the height data is calculated. The accumulative addition of the height data is executed and suspended in response to the calculated variation in the height data. A decision is made as to whether the solder portion is acceptable or unacceptable on the basis of a result of the accumulative addition.
U.S. Pat. No. 4,650,333 discloses a non-contact system for detecting printed circuit wiring defects and for measuring circuit feature height relative to a substrate. The system has an energy source for illuminating the substrate and circuit features and a scanner for both instantaneously receiving energy reflected from the substrate and circuit features and for generating a signal in response to the reflected energy, which signal is adapted to vary with the intensity of the reflected energy. An analyzer is connected to the scanner for correlating the generated signal to a measurement representative of the height of the circuit features relative to the substrate. Variations and non-uniformity of the substrate surface due to bending, warpage or other causes can be accounted for so as to provide an accurate measurement of the height of a circuit feature relative to the substrate surface on which it is mounted.
According to U.S. Pat. No. 4,957,369, automatic acquisition and analysis for three-dimensional surface geometries is accomplished by use of an opto-electronic technique which exploits large-linear-area lateral-photo-effect-diodes and employs a reflected, tightly focused light spot. The technique consists of one very small light spot pulsed for example at 10,000 Hertz with a 50% duty cycle. The light spot is focused on the surface to be measured and scanned. The diode detectors, mounted in the focal plane of a pair of cameras, return azimuth and elevation information for each spot. Knowledge of the location and orientation of the cameras, as well as calibration corrections for each camera, completes the information necessary to reconstruct the full three-dimensional location of each reflected light spot.